Stereotactic body radiotherapy for local boost irradiation in unfavourable locally recurrent gynaecological cancer

Purpose

To evaluate outcome of radiotherapy for locally recurrent cervical and endometrial cancer.

Materials and methods

Nineteen patients were treated for a locally recurrent cervical (n = 12) or endometrial (n = 7) cancer median 26 months after initial surgery (n = 18) or radiotherapy (n = 1). The whole pelvis was irradiated with 50 Gy conventionally fractionated radiotherapy (n = 16). Because of large size of the recurrent cancer (median 4.5 cm) and peripheral location (n = 12), stereotactic body radiotherapy (SBRT; median 3 fractions of 5 Gy to 65%) was used for local dose escalation instead of (n = 16) or combined with (n = 3) vaginal brachytherapy.

Results

After median follow-up of 22 months, 3-year overall survival was 34% with systemic progression the leading cause of death (7/10). Median time to systemic progression was 16 months. Three local recurrences resulted in a local control rate of 81% at 3 years. No correlation between survival, systemic or local control and any patient or treatment characteristic was observed. The rate of late toxicity > grade II was 25% at 3 years: two patients developed a grade IV intestino-vaginal fistula and one patient suffered from a grade IV small bowel ileus.

Conclusion

Image-guided SBRT for local dose escalation resulted in high rates of local control but was associated with significant late toxicity.     

Double-scattered proton-based stereotactic body radiotherapy for stage I lung cancer: A dosimetric comparison with photon-based stereotactic body radiotherapy

Purpose

Stereotactic body radiotherapy (SBRT) has gained popularity in the treatment of early-stage non-small-cell lung cancer (NSCLC) because of its ability to deliver conformal radiation doses to small targets. However, photon-based SBRT (xSBRT) is associated with significant grade 3+ toxicities. In this study, we compare xSBRT treatment plans with proton-based SBRT (pSBRT) to determine whether dose to normal structures could be reduced if SBRT was delivered with protons.

Materials and methods

Eight patients with medically inoperable, peripherally located stage I NSCLC were treated with xSBRT to 48 Gy in 4 12-Gy fractions. These patients were retrospectively re-planned using the same treatment volumes with 3-dimensional conformal double-scatter proton therapy. A Wilcoxon paired test compared dosimetric parameters between the plans for each patient.

Results

Compared with xSBRT there was a dosimetric improvement with pSBRT for these volumes: lung V5 (median difference [MD] = 10.4%, p = 0.01); V10 (MD = 6.4%, p = 0.01); V20 (MD = 2.1%, p = 0.01); V40 (MD = 1.5%, p = 0.05); and mean lung dose (MD = 2.17 Gy, p = 0.01). There were also benefits (p = <0.05) in D0.1cm3 and D5cm3 with pSBRT to the heart, esophagus, and bronchus.

Conclusions

In a dosimetric comparison between photon and proton-based SBRT, protons resulted in lower doses to critical organs at risk and a smaller volume of non-targeted normal lung exposed to radiation (V5, V10, V20, and V40). The clinical significance and relevance of these dosimetric improvements remain unknown.     

Stereotactic radiotherapy with real-time tumor tracking for non-small cell lung cancer: Clinical outcome

Purpose

To report the clinical outcome of treatment using real-time tumor tracking for 70 patients with inoperable stage I non-small cell lung cancer (NSCLC).

Materials and methods

Seventy inoperable patients with peripherally located early-stage NSCLC were treated with 45 or 60 Gy in three fractions using CyberKnife. Pathology was available in 51% of patients. Thirty-nine patients had a T1-tumor and 31 had a T2-tumor. Markers were placed using the vascular, percutaneous intra-, or extra-pulmonary approach, depending on the risk of pneumothorax.

Results

The actuarial 2-year local control rate for patients treated with 60 Gy was 96%, compared to 78% for patients treated with a total dose of 45 Gy (p = 0.197). All local recurrences (n = 4) occurred in patients with T2-tumors. Overall survival for the whole group at two years was 62% and the cause specific survival was 85%. The median follow-up was 15 months. Grade 3 toxicity occurred in two patients (3%) after marker placement. Treatment-related late grade 3 toxicity occurred in 7 patients (10%). No grade ?4 toxicity occurred.

Conclusion

Excellent local control of 96% at 1- and 2-years was achieved using 60 Gy in three fractions for NSCLC patients treated with the real-time tumor tracking. Toxicity was low.     

Impact of PARP-1 and DNA-PK expression on survival in patients with glioblastoma multiforme

Purpose

To analyze, whether higher tumor levels of DNA repair enzymes contribute to worse treatment results of glioblastoma multiforme (GBM) patients after postoperative radiotherapy.

Materials and methods

Thirty four patients with GBM received postoperative radiotherapy. Tumor sections were examined for poly-ADP ribose polymerase-1 (PARP-1) and DNA protein kinase (DNA-PK) expression. Immunohistochemical staining intensities of PARP-1 and DNA-PK were determined (score 0-3) and expression levels were correlated with patients overall survival.

Results

Median survival time of the whole study group was 10.0 months (95% CI 8.1-11.9). Median survival of patients with high and low (?median and <median) tumor PARP-1 levels were 10.0 months (95% CI 7.9-12.1) and 12.0 months (95% CI 8.3-15.7), respectively (p = 0.93). In contrast, median survival of patients with high and low tumor DNA-PK levels were 9.0 months (95% CI 7.2-10.8) and 13.0 months (95% CI 10.7-15.3), respectively (p = 0.02). In multivariate analysis, DNA-PK expression emerged as a significant independent predictor for overall survival (HR 3.9, 95% CI 1.5-10.7, p = 0.01).

Conclusion

This hypothesis generating study showed that high tumor levels of DNA-PK correlate with poor survival of GBM patients. Further studies are needed to confirm these results and to clarify whether DNA-PK inhibitors might have a potential to radiosensitize GBM and improve the treatment outcome of this devastating disease.     

Prognostic effect of stromal lymphocyte infiltration in thymic carcinoma

Background

The purpose of this study was to clarify the relationship between the tumor infiltrating lymphocytes and clinical outcome in patients with thymic carcinoma.

Methods

Tissue specimens from 32 patients who underwent surgical resection for thymic carcinoma were immunohistochemically analyzed for CD4, CD8 and CD20 expression.

Results

Tumor-infiltrating lymphocytes were generally more abundant in the stroma. The patients with low CD4+ lymphocytes (p = 0.037) and low CD20+ lymphocytes (p = 0.045) within tumor stroma showed poor survival. Furthermore, concurrent low levels of CD4+ and CD20+ (p = 0.014), CD8+ and CD20+ (p = 0.025), and, CD4+, CD8+, and CD20+ (p = 0.025) in tumor stroma were significantly associated with poor prognosis when compared to the others group.

Conclusion

Our results indicate that infiltrating CD4+, CD8+, and CD20+ lymphocytes in cancer stroma may cooperate to suppress cancer progression and their presence together appear to be prognostic factor in thymic carcinoma.     

Pulmonary oligometastases: Metastasectomy or stereotactic ablative radiotherapy?

Background and purpose

Stereotactic ablative radiotherapy (SABR; or stereotactic body radiotherapy, SBRT) emerges as treatment option for pulmonary oligometastatic disease (OMD), but there are no studies comparing SABR with pulmonary metastasectomy (PME). We analysed consecutive patients referred via a university-hospital based multidisciplinary team.

Material and methods

Patients were offered PME as first choice and SABR in case they were considered to be less suitable surgical candidates. Overall survival was the primary endpoint. Secondary endpoints were progression-free-survival, local control of treated metastases, and freedom-from-failure of a local-only treatment strategy without systemic therapy.

Results

From 2007 until 2010, 110 patients were treated and analysed (PME, n = 68; SABR, n = 42). Median follow-up time was 43 months (minimally, 25). Estimated overall survival rates at one, three, and five years were 87%, 62%, and 41% for PME, and 98%, 60%, and 49% for SABR, respectively (logrank-test, p = 0.43). Local control at two years was 94% for SABR and 90% for PME. Progression-free survival was 17% at three years, but 43% of the patients still had not failed a local-only treatment strategy.

Conclusions

Although SABR was second choice after PME, survival after PME was not better than after SABR. Prospective comparative studies are clearly required to define the role of both, SABR and PME in OMD.     

Impact of target volumes and radiation technique on loco-regional control and survival for patients with unilateral cervical lymph node metastases from an unknown primary

Purpose

To compare the impact of an unilateral post-operative irradiation or a bilateral irradiation in terms of loco-regional control and survival in patients with cervical lymph node of squamous cell carcinoma from an unknown primary (CUP).

Methods and materials

Ninety five patients with epidermoid carcinoma involving unilateral cervical lymph nodes from an unknown primary were treated in two institutions from 1990 to 2007. Post-operative radiation therapy was delivered to one side of the neck in 59 cases, to both sides of the neck in 36 cases. There were 11 women and 84 men ranging in age from 38 to 80 years (median 59 years). Neck dissection was performed in 79 patients while 16 patients underwent single lymph node sampling only.

Results

After a median follow-up of 3.3 years, the nodal relapse rate was 34% after unilateral neck irradiation and 25% after bilateral radiotherapy (p = 0.21). Six contralateral lymph node relapses occurred after unilateral irradiation (10%). The 5-year overall survival rate of the entire group was 24%. The 5-year OS rates were 22% after unilateral irradiation and 23%, after bilateral radiotherapy (p = 0.944). The occult primary occurred in 12% after unilateral irradiation and 6% after bilateral radiotherapy. The radiation technique (3D-CRT or IMRT vs. 2D: p = 0.026) was prognostic on loco-regional control. Independent prognostic determinants on overall survival were the WHO status (p = 0.013) and the radiation technique (2D vs. 3D-CRT or IMRT; p = 0.029). There was no difference in loco-regional control (p = 0.639) and no difference in survival (p = 0.493) when chemotherapy was associated.

Conclusions

Retrospective comparisons between bilateral and unilateral neck radiotherapies did not show differences in terms of loco-regional control and survival. However, patient’s local regional control and survival are significantly improved after 3D-CRT or IMRT.     

The maximum standardized uptake value (SUVmax) on FDG-PET is a strong predictor of local recurrence for localized non-small-cell lung cancer after stereotactic body radiotherapy (SBRT)

Background

The maximum standardized uptake value (SUVmax) of FDG-PET may predict local recurrence for localized non-small-cell lung cancer (NSCLC) after stereotactic body radiotherapy (SBRT).

Methods

Among 195 localized NSCLCs that were treated with total doses of either 40 Gy or 50 Gy in 5 SBRT fractions, we reviewed those patients who underwent pre-treatment FDG-PET using a single scanner for staging. Local control rates (LCRs) were obtained by the Kaplan-Meier method and a log-rank test. Prognostic significance was assessed by univariate and multivariate analyses.

Results

A total of 95 patients with 97 lesions were eligible. Median follow-up was 16.0 months (range: 6.0-46.3 months). Local recurrences occurred in 9 lesions. By multivariate analysis, only the SUVmax of a primary tumor was a significant predictor (p = 0.002). Two years LCRs for lower SUVmax (<6.0; n = 78) and higher SUVmax (?6; n = 19) were 93% and 42%, respectively. In subgroups with T1b and T2, LCRs were significantly better for lower SUVmax than for higher SUVmax (p < 0.0005 and p < 0.01). In both subgroups that received 40 Gy and 50 Gy, LCRs were also significantly better for lower SUVmax than for higher SUVmax (p < 0.001 and p < 0.01).

Conclusions

SUVmax was the strongest predictor for local recurrence. A high SUVmax may be considered for dose escalation to improve local control. Additional follow-up is needed to determine if SUVmax is correlated with regional recurrence, distant metastasis, and survival.     

The use of palliative radiotherapy for bone metastasis

Background

The value of palliative radiotherapy (PRT) for bone metastases is well established, but little is known about its use in the general population.

Purpose

To describe the use of PRT for bone metastases in Ontario.

Materials and methods

This was a retrospective cohort study. Treatment records from all Ontario RT departments were linked to a population-based cancer registry to describe the use of PRT.

Results

12.2% of the 434,241 patients, who died of cancer in Ontario between 1984 and 2004, received at least one course of PRT for bone metastases in the last 2 years of life. The rate of use of PRT varied across the province (inter-county range, 8.2-18.6%). Older patients and residents of poorer areas were less likely to receive PRT (p < 0.0001). Patients diagnosed with cancer in a hospital with a radiotherapy facility and those who lived closer to a radiotherapy centre were more likely to receive PRT (p < 0.0001). Over the study period, the use of PRT decreased in breast cancer and myeloma, but increased in prostate cancer (p < 0.0001).

Conclusions

Access to PRT appears to be inequitable. More effort is required to make this useful treatment available to all those who would benefit from it.     

Co-morbidity index predicts for mortality after stereotactic body radiotherapy for medically inoperable early-stage non-small cell lung cancer

Purpose

To determine the prognostic role of co-morbidity in medically inoperable early-stage non-small cell lung cancer (NSCLC) treated with stereotactic body radiotherapy (SBRT).

Methods and materials

Between 2000 and 2007, 88 consecutive early-stage medically inoperable NSCLC patients were treated by linac-based SBRT. The dose was either 45 Gy or 67.5 Gy in three fractions prescribed to the isocenter. Baseline co-morbidities were retrospectively retrieved by consultation of a formal electronic registry of diagnoses as well as patients’ charts. The age-adjusted Charlson Co-morbidity Index (CCI) was scored for each patient and subjected to univariate and multivariate analysis.

Results

With a median follow-up of 44 months, the actuarial local control rate at 4 years was 89% while the median overall survival was 22 months. The median age-adjusted CCI score was 5. The age-adjusted CCI was a significant predictor of overall survival on both univariate (p = 0.002) and multivariate analysis (p = 0.011). Patients with an age-adjusted CCI score of 3 or less had a median survival of 41 months versus only 11 months for those scoring 6 or more.

Conclusion

The number and seriousness of co-morbidities predict overall survival in medically inoperable early-stage NSCLC treated with SBRT. Because the determination of medical operability is frequently based on both objective measures and subjective clinical judgment, it is recommended that co-morbidity be formally indexed in all studies examining the outcomes of SBRT.     

Adjuvant chemoradiotherapy with or without intraoperative radiotherapy for the treatment of resectable locally advanced gastric adenocarcinoma

Purpose

To document the long-term efficacy of intraoperative electron radiotherapy (IOERT) followed by concurrent chemotherapy and external-beam radiotherapy (EBRT) in the management of locally advanced gastric cancer.

Materials and methods

A total of 97 consecutive patients with T3/4 or N+ gastric adenocarcinoma were enrolled. Fifty-one patients received adjuvant chemoradiotherapy (EBRT group) and 46 received IOERT (dose range, 12-15 Gy) followed by chemoradiotherapy (EBRT + IOERT group).

Results

The 5-year locoregional control rates were 50% and 35% in the two groups with or without IOERT, respectively (p = 0.04). Two patients had recurrence within the IOERT field in the EBRT + IOERT group and 14 patients recurred in the same area in the EBRT group (p = 0.02). Multivariate analyses revealed that adjuvant IOERT was an independent prognosticator for both local-regional control (p = 0.02) and disease-free survival (p = 0.05). G3/4 late toxicity was observed in 5 patients in the EBRT + IOERT group, but none in the EBRT group (p = 0.02).

Conclusions

Higher radiation dose may contribute to the improvement of local control, especially in the field encompassed by IOERT. The addition of IOERT to surgery and adjuvant chemoradiation deserves further investigation in a randomized trial.     

Volumetric modulated arc therapy versus conventional intensity modulated radiation therapy for stereotactic spine radiotherapy: A planning study and early clinical data

Background and purpose

Outcomes for selected patients with spinal metastases may be improved by dose escalation using stereotactic body radiation therapy (SBRT). As target geometry is complex, we compared SBRT plans using volumetric modulated arc radiotherapy (RapidArc®, RA) and conventional intensity-modulated radiotherapy (IMRT).

Materials and methods

RA and IMRT plans to deliver a fraction of 16 Gy to at least 90% of planning target volume (PTV) were compared for PTV coverage, normal organ sparing and estimated delivery times. Group 1 consisted of PTVs to only vertebral body (n = 3), while group 2 had PTVs encompassing the entire vertebra (n = 4). Finally, RA delivery parameters in four patients were assessed.

Results

Both techniques delivered 16 Gy to a mean of 95% and 85% of the PTV in groups 1 and 2, respectively. Spinal cord sparing was comparable; mean V_{10-partial cord} for RA and IMRT in group 1 was 3.6%, and was 9.4% versus 11.5%, respectively, in group 2. Estimated mean treatment times for RA with 2-3 arcs and IMRT were comparable. Clinical RA beam-on times ranged from 11 to 15.4 min.

Conclusions

Both RA and conventional IMRT plans deliver high quality vertebral SBRT, but plan quality was poorer when the PTV consisted of the entire vertebra.     

4D-CT-based target volume definition in stereotactic radiotherapy of lung tumours: Comparison with a conventional technique using individual margins

Purpose

To investigate the dosimetric benefit of integration of 4D-CT in the planning target volume (PTV) definition process compared to conventional PTV definition using individual margins in stereotactic body radiotherapy (SBRT) of lung tumours.

Material and methods

Two different PTVs were defined: PTV_conv consisting of the helical-CT-based clinical target volume (CTV) enlarged isotropically for each spatial direction by the individually measured amount of motion in the 4D-CT, and PTV_4D encompassing the CTVs defined in the 4D-CT phases displaying the extremes of the tumour position. Tumour motion as well as volumetric and dosimetric differences and relations of both PTVs were evaluated.

Results

Volumetric examinations revealed a significant reduction of the mean PTV by 4D-CT from 57.7 to 40.7 cm³ (31%) (p < 0.001). A significant inverse correlation was found for the motion vector and the amount of inclusion of PTV_4D in PTV_conv (r = −0.69, 90% confidence limits: −0.87 and −0.34, p = 0.007). Mean lung dose (MLD) was decreased significantly by 17% (p < 0.001).

Conclusions

In SBRT of lung tumours the mere use of individual margins for target volume definition cannot compensate for the additional effects that the implementation of 4D-CT phases can offer.     

Stereotactic body radiotherapy (SBRT) for oligometastatic lung tumors from colorectal cancer and other primary cancers in comparison with primary lung cancer

Purpose

To analyze local control of oligometastatic lung tumors (OLTs) compared with that of primary lung cancer after stereotactic body radiotherapy (SBRT).

Materials and methods

Retrospective record review of patients with OLTs who received SBRT with 50 Gy in 5 fractions. Local control rates (LCRs), toxicities, and factors of prognostic significance were assessed.

Results

Twenty-one colorectal OLTs, 23 OLTs from other origins, and 188 primary lung cancers were included. Multivariate analysis revealed only tumor origin was prognostically significant (p < 0.05). The 1-year/2-year LCRs in colorectal OLTs and OLTs from other origins were 80%/72% and 94%/94%, respectively. The LCR in colorectal OLTs was significantly worse than that in OLTs from the other origins and primary lung cancers with pathological and clinical diagnosis (p < 0.05, p < 0.0001 and p < 0.005). Among 44 OLT patients, Grades 2 and 3 radiation pneumonitis were identified in 2 and 1 patients, respectively. No other toxicities of more than Grade 3 occurred.

Conclusion

SBRT for OLTs is tolerable. The LCR for OLTs from origins other than colorectal cancer is excellent. However, LCR for colorectal OLTs is worse than that from other origins. Therefore dose escalation should be considered to achieve good local control for colorectal OLTs.     

High-dose radiotherapy or concurrent chemo-radiation in lung cancer patients only induces a temporary, reversible decline in QoL

Background and purpose

Aggressive radiotherapy or concurrent chemo-radiation therapy for lung cancer leads to a high incidence of severe, mostly esophageal, toxicity. The purpose of this study was to investigate the evolution of quality of life (QoL) in patients with lung cancer, selected for curative radiotherapy (RT) or chemo-RT.

Methods

Seventy-five lung cancer patients completed a longitudinal the EORTC QLQ-C30 and LC13. Linear mixed regression models were fitted to investigate the impact of different factors on overall QoL.

Results

Overall QoL decreased shortly after the end of RT (4 points, p = 0.19), but increased back to baseline within 3 months. Mean scores of role functioning (p = 0.018), cognitive functioning (p = 0.002), dyspnoea (EORTC QLQ-LC13; p = 0.043), dysphagia (p = 0.005) and hoarseness (p = 0.029), showed a significant worsening over time. Emotional functioning (p = 0.033) improved significantly over time.Severe esophagitis (?grade 2) was reported in only 12% of the patients. Next to maximal esophageal toxicity ?grade 2 (p = .0.010), also tumor stage IIIA (p < 0.001), tumor stage IIIB (p = 0.003), gender (p = 0.042) and fatigue (p < 0.001) appeared to be significant predictors of QoL.

Conclusion

High-dose radiotherapy or concurrent chemo-radiation in the treatment of lung cancer seems to be a well-tolerated treatment option with preservation of QoL.     

Stereotactic body radiotherapy for unresectable cholangiocarcinoma

Purpose

To report outcomes of a single institution study of stereotactic body radiotherapy (SBRT) for unresectable cholangiocarcinoma. The dose-volume dependency of the observed gastrointestinal toxicity is explored.

Methods and materials

Twenty-seven patients with unresectable cholangiocarcinoma (n = 26 Klatskin tumours and one intrahepatic cholangiocarcinoma (IHCC)) were treated by linac-based SBRT. The dose schedule was 45 Gy in three fractions prescribed to the isocenter.

Results

The median progression-free survival and overall survival were 6.7 and 10.6 months, respectively. With a median follow-up of 5.4 years, 6 patients had severe duodenal/pyloric ulceration and 3 patients developed duodenal stenosis. Duodenal radiation exposure was higher in patients developing moderate to high-grade gastrointestinal toxicity with the difference in mean maximum dose to 1 cm³ of duodenum reaching statistical significance. A statistically significant association between grade ? 2 ulceration and volume of duodenum exposed to selected dose levels was not established.

Conclusion

The outcomes of SBRT for unresectable cholangiocarcinoma appear comparable to conventionally fractionated chemoradiotherapy with or without brachytherapy boost. The practical advantages of SBRT are of particular interest for such poor prognosis patients. Patient selection, however, is key in order to avoid compromising such practical gains with excessive gastrointestinal toxicity.     

Toxicity after reirradiation of pulmonary tumours with stereotactic body radiotherapy

Purpose

To assess toxicity and feasibility of reirradiation with stereotactic body radiotherapy (SBRT) after prior lung SBRT for primary lung cancer or lung metastases.

Patients and materials

Twenty-nine patients reirradiated with SBRT on 32 lung lesions (11 central, 21 peripheral) were retrospectively reviewed. Median follow-up time was 12 months (range 1-97). The primary endpoint was toxicity, secondary endpoints were local control and overall survival time. Toxicity was scored according to the NCI-CTCAE version 3.

Results

Grade 3-4 toxicity was scored 14 times in eight patients. Three patients died because of massive bleeding (grade 5). Larger clinical target volumes (CTV) and central tumour localization were associated with more severe toxicity. There was no correlation between mean lung dose (MLD) and lung toxicity. Local control at 5 months after reirradiation was 52%, as assessed by CT-scan (n = 12) or X-thorax (n = 3). A larger CTV was associated with poorer local control. Kaplan-Meier estimated 1- and 2-year survival rates were 59% and 43%, respectively.

Conclusions

Reirradiation with SBRT is feasible although increased risk of toxicity was reported in centrally located tumours. Further research is warranted for more accurate selection of patients suitable for reirradiation with SBRT.     

A study on the dosimetric accuracy of treatment planning for stereotactic body radiation therapy of lung cancer using average and maximum intensity projection images

Purpose

To assess the accuracy of current stereotactic body radiation therapy (SBRT) lung treatment planning methodologies on irregular breathing patterns, we have performed a systematic dosimetric evaluation in phantoms by utilizing maximum intensity projection (MIP) and average (AVG) images generated from four dimensional computed tomography (4DCT).

Methods

A custom built programmable lung phantom was used to simulate tumor motions due to various breathing patterns of patients. 4DCT scans were obtained in helical mode, and reconstructed AVG and MIP datasets were imported into the Pinnacle 8.0 h treatment planning system. SBRT plans were generated and executed, and delivered doses were measured by radiochromic film for analysis.

Results

For targets moving regularly or irregularly within a small range (7.0 ± 1.8 mm, n = 6), we observed good agreement between the measured and computed dose distributions. However, for targets moving irregularly with a larger range (20.8 ± 2.6 mm, n = 4), the measured isodose lines were found to be shifted relative to the planned distribution, resulting in an under-dosing (over 10%) in a portion of the PTV. We further observed that the discrepancy between planned and measured dose distribution is due to the inaccurate representation of irregular target motion in the MIP images generated from 4DCT.

Conclusions

Caution should be used when planning from 4DCT images in the presence of large and irregular target motion. The inaccuracy inherent in 4DCT MIP and AVG images can be mitigated through the application of methodologies to reduce respiratory motion, such as abdominal compression, and through the use of volumetric image guidance (e.g., cone beam CT - CBCT) to assure precise targeting with minimal shifts.     

Comparative study of respiratory motion correction techniques in cone-beam computed tomography

Background and purpose

To validate the clinical usefulness of motion-compensated (MC) cone-beam (CB) computed tomography (CT) for image-guided radiotherapy (IGRT) in comparison to four-dimensional (4D) CBCT and three-dimensional (3D) CBCT.

Material and methods

Forty-eight stereotactic body radiation therapy (SBRT) patients were selected. Each patient had 5-12 long CB acquisitions (4 min) and 1-7 short CB acquisitions (1 min), with a total of 349 and 150 acquisitions, respectively. 3D, 4D and MC CBCT images of every acquisition were reconstructed. Image quality, tumor positioning accuracy and tumor motion amplitude were quantified.

Results

The mean image quality of long short acquisitions, measured using the correlation ratio with the planning CT, was 74%/70%, 67%/47% and 79%/74% for 3D, 4D and MC CBCT, respectively; both 4D and MC CBCT were corrected for respiratory motion artifacts but 4D CBCTs suffered from streak artifacts. Tumor positioning with MC CBCT was significantly closer to 4D CBCT than 3D CBCT (p < 0.0001). Detailed patient analysis showed that motion correction was not required for tumors with less than 1 cm motion amplitude.

Conclusions

4D and MC CBCT both allow accurate tumor position analysis under respiratory motion but 4D CBCT requires longer acquisition time than MC CBCT for adequate image quality. MC CBCT can therefore advantageously replace 4D CBCT in clinical protocols for patients with large motion to improve image quality and reduce acquisition time.